Root canal treatment

ABSTRACT

A device for disinfecting and/or sterilization of a dental cavity includes: an electrode pair that extends into the cavity to provide current along a portion of the cavity; and a controller that sends controlled electrical energy to the cavity via current flowing between the electrodes when located in the cavity, thereby to provide electrical energy for disinfection and/or sterilization.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/773,061, filed on May 4, 2010, which is continuation-in-part (CIP) ofPCT Patent Application No. PCT/IL2009/001048 having International FilingDate of Nov. 5, 2009, which claims the benefit of priority of U.S.Provisional Patent Application No. 61/193,204 filed on Nov. 5, 2008. Thecontents of the above applications are all incorporated by reference asif fully set forth herein in their entirety.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a device and method for treatment of adental cavity such as a root canal and, more particularly, but notexclusively to a device for sterilizing a root canal.

A root canal is the commonly used term for the main canals within thedentine of the tooth. These are part of the natural cavity within atooth that consists of the dental pulp chamber, the main canals, andsometimes more intricate anatomical branches that may connect the rootcanals to each other or to the root surface of the tooth. Root canalsare filled with a highly vascularized, loose connective tissue, thedental pulp. This sometimes becomes infected and inflamed, generally dueto caries or tooth fractures that allow microorganisms, mostly bacteriafrom the oral flora or their byproducts, access to the pulp chamber orthe root canals. The infected tissue is removed by a surgicalintervention known as endodontic therapy, more commonly known as rootcanal treatment.

Removal and disinfection procedures are not always effective at removingindividual bacteria, but it is even more difficult to remove bacterialfilms. Nevertheless complete removal of bacteria or sterilization of thecanal prior to sealing the root canal is a necessary condition for asuccessful outcome to the treatment.

Known systems insert cleaning (disinfecting) fluids into the root canalbut such fluids are highly toxic. Furthermore they have to be present inthe root canal for a relatively large amount of time. In addition thefluid must reach every part of the root canal, something which cannot beguaranteed. In some cases, particularly where infection is alreadypresent, the treatment must be repeated several times before the rootcanal can be sealed. The method takes time and depends very much on theexpertise of the dentist carrying out the treatment.

A further disadvantage of the above system is that bubbles or airpockets tend to occur, especially in the deeper parts of the root canalor where root canal passages are not straight, and the air pockets tendto prevent the cleaning fluid from making contact with all surfaces.

Other systems place an electrode inside the root canal and anotherelectrode outside the tooth and pass a current between the two, closingthe circuit via the human body. The electromagnetic field and in somecase the temperature kills bacteria, but the effectiveness is limitedbecause often the conditions in the canal are not ideal. This isparticularly the case when the electrode is far from the apical aria.One version uses 500 Watts of power, at a frequency of 300-KHz, in orderto create a current path from the apical aria of the root canal to theexternal electrode, through the patient's flesh. A disadvantage of thissystem is that much of the power provided goes to setting up the currentpath and not to carrying out the sterilization. Furthermore thesterilization effect is not uniform over the root canal, and requiresexceptional skill on the part of the dentist in order to be successful.Furthermore the resistance provided by the human body varies betweenindividuals, making it impossible to control the power level in givencases. Thus a higher than designed resistance may reduce the output andvice versa. Furthermore the power increases with proximity to the apicalaria, due to the reduced distance between the two ends of the probe orelectrode and in some cases a current overload may result, causing painto the patient. Thus it is impossible to control the power and you mayeither expose the client to sharp, pain or you may fail to providesufficient power to destroy all the bacteria.

In particular, efforts to ensure that the effect is evenly distributedover the root canal are complicated by the need to avoid the root canalapex. The apex contains healthy tissue which should not be damaged.

There is thus a widely recognized need for, and it would be highlyadvantageous to have, a method of root canal sterilization that isdevoid of the above limitations.

SUMMARY OF THE INVENTION

According to some embodiments of a first aspect of the present inventionthere is provided a device for disinfecting and/or sterilization of adental cavity comprising:

-   -   an electrode pair adapted to extend into said cavity to provide        current along at least a portion of the cavity; and    -   a controller configured for sending controlled electrical energy        to said cavity via current flowing between the electrodes when        located in said cavity, thereby to provide electrical energy for        said disinfection and/or sterilization.

In an embodiment of the invention a first electrode of said electrodepair forms a central axis and a second electrode of said electrode pairis coiled about said central axis.

Optionally, said first electrode is controllably extendable along saidaxial direction, thereby to vary a length of a gap between said firstelectrode and said second electrode.

Optionally, said controller is configured to adjust a level of energyreleased within said cavity.

In an embodiment of the invention, the level of energy is limited inaccordance with a tooth cavity resistance.

Optionally, the device further comprises a plug for closure of saidcavity. Optionally, the plug is movable to define a depth to which saidelectrode pair extends into said cavity.

Optionally, the controller configured to detect whether the cavitycontains conductive fluid, said detecting comprising measuringconductivity between the electrodes.

Optionally, the controller is configured to cut off said current if theabsence of said fluid is detected in said cavity.

In an embodiment of the invention, the device is configured with an apexdetection unit for detecting the distance of an apex of said cavity fromsaid electrode pair. Optionally, the controller disables pulsegeneration when the electrode is at the apex.

Optionally, the controller comprises a pulse generator. Optionally, thedevice comprises a resistance measurement unit for measuring electricalresistance between said electrode pair. Optionally, the controller isoperatively connected to said resistance measurement unit, and shuts offsaid controlled current whenever said electrical resistance is at alevel indicating that said electrodes are not currently located in saidcavity or the cavity does not contain a liquid

There is further provided, in accordance with an embodiment of theinvention, a method of treatment of a dental cavity comprising:

-   -   inserting a pair of electrodes into said cavity; and    -   generating a controlled energy pulse between said electrodes, in        an amount suitable for sterilizing and/or disinfecting said        cavity.

In an embodiment of the invention the method includes filling saidcavity with a conductive fluid prior to said generating a controlledenergy pulse. Optionally, the method includes providing a pulse to drytissues within said cavity for removal.

In an embodiment of the invention, the method includes measuring alocation of an apex of said cavity and setting a mechanical limiter toprovide insertion of said electrodes a controlled distance into saidcavity responsive to said apex location measurement.

In an embodiment of the invention, the energy is according to a localvolume of said cavity.

In an embodiment of the invention, the method includes locating theelectrode pair at a first depth in said cavity and providing an energypulse thereat and then relocating said electrodes to a second depth andan providing an energy pulse thereat.

Optionally, conductive fluid comprises a salt solution. Optionally, thesalt solution comprises a salt concentration lying between 0.9% andsaturation. Optionally the salt concentration comprises any one of thegroup comprising a 2% solution, a 3% solution, a 4% solution, a 5%solution, a 6% solution, a 7% solution, an 8% solution, a 9% solution, a10% solution, an 11% solution, a 12% solution, a 13% solution, a 14%solution, a 15% solution, a 16% solution, a 17% solution, an 18%solution, a 19% solution, and a 20% solution.

Optionally, the conductive fluid comprises one or more ofethylenediaminetetraacetic acid (EDTA hydrogen peroxide, EDTA,chlorhexidine or iodoform (IKI—potassium iodide).

In an embodiment of the invention, the energy pulse causes a breakdownin the cavity that is limited to the cavity.

There is further provided, in accordance with an embodiment of theinvention, a method of treatment of a cavity comprising:

inserting a pair of electrodes into said cavity; and

generating controlled energy between said electrodes, and therewithdisinfecting and/or sterilizing said cavity.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. The materials, methods, andexamples provided herein are illustrative only and not intended to belimiting.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings. With specific reference now tothe drawings in detail, it is stressed that the particulars shown are byway of example and for purposes of illustrative discussion of thepreferred embodiments of the present invention only, and are presentedin order to provide what is believed to be the most useful and readilyunderstood description of the principles and conceptual aspects of theinvention. In this regard, no attempt is made to show structural detailsof the invention in more detail than is necessary for a fundamentalunderstanding of the invention, the description taken with the drawingsmaking apparent to those skilled in the art how the several forms of theinvention may be embodied in practice.

In the drawings:

FIG. 1 is a simplified diagram illustrating a first device according toan embodiment of the present invention where electrodes are insertedinto a root canal;

FIG. 2 shows both a detail and an exploded diagram of the electrodeassembly of the device of FIG. 1;

FIG. 3A is a simplified cross section of the handle and electrode movingmechanism of the device of FIG. 1;

FIG. 3B is an alternative version of the electrode moving assembly ofFIG. 3A allowing for multiple electrode positions;

FIG. 4 is another simplified diagram showing the cross section comparedto the complete assembly and against the various assemblies separatedfrom each other;

FIG. 5 is a simplified diagram showing the device of FIG. 1 withattachments for apex location, according to another embodiment of thepresent invention;

FIG. 6 is a simplified diagram showing in greater detail the electrodeassembly of FIG. 1 in the root canal;

FIG. 7 is a simplified flow chart showing the operation of a deviceaccording to an embodiment of the present invention;

FIG. 8 is a simplified diagram showing the device in the two differentpositions for the first and second pulse trains respectively accordingto an embodiment of the present invention; and

FIG. 9 is a simplified schematic diagram which shows use of attachmentsfor apex location in order to set the position of the electrode in theroot canal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present embodiments comprise an apparatus and a method for rootcanal sterilization using electrical energy, where an electrode pair isinserted into the root canal. A discharge is induced between theelectrodes of the electrode pair. The current is confined to the rootcanal, and electrical energy is therefore kept out of surroundingtissues. The result is that several Joules of energy can be releasedwithin the root canal to kill the bacteria, without detrimental effecton the human body

The effect can be enhanced by filling the root canal with either aconductive fluid, such as salt water or an irrigation fluid such as 17%ethylenediaminetetraacetic acid (EDTA), to take two examples. Otherfluids with high conductivity and/or sterilizing or disinfecting abilitymay also be considered. Mixtures of conducting materials and sterilizingor disinfection agents may also be used. In an embodiment of theinvention a conductive fluid is placed in the root canal and theelectrode pair is dipped or otherwise contacted with a sterilizing ordisinfecting fluid. The electrode pair is then inserted into theconducting liquid in the root canal and the current is made to flowbetween the electrodes. Other sterilizing or disinfecting solutions canbe used. Applicants believe that hydrogen peroxide, chlorhexidine,iodoform (IKI—potassium iodide are suitable.

In an embodiment the electrical energy diffuses into the root canalvolume and kills the bacteria. The bacteria are killed by one or more ofan electromagnetic wave, a wave of heat provided via the liquid and apressure wave. Although any one of the above may be useful, two or moreare preferred for clinical effectiveness and all three together providethe ideal sterilization, thus providing the sterilization.

It is believed that an important factor in the sterilization process isaggressive oxidation cause by the break-up of the water in the solutionin which one component is atomic oxygen. The resulting oxidation is verystrong compared to that resulting from mere high temperatures. Thebreakdown caused by the pulse gives rise to pressure and thermal waveswhich force the atomic oxygen particles into side tubules and channelsin the interior of the root. It is believed that many of these tubulesand channels are not open during normal sterilization.

Furthermore the electric current generated between the electrodes can beconcentrated mainly between the two electrode tips, so the use of energycan be tightly controlled. Thus given precise placing of the electrodesin the root canal it is possible to provide energy at precise locationsin the root canal and to vary the energy in accordance with thelocations. Furthermore since there is no need to generate an electricalpath through the Apex or the tissues of the gums, the energy level canbe tailored for the particular location within the canal according tothe canal volume and shape.

The principles and operation of an apparatus and method according to thepresent invention may be better understood with reference to thedrawings and accompanying description.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangement of the components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting. It should also beunderstood that for simplicity some features are described only withrespect to some embodiments. However, combinations of elements fromdifferent embodiments are also included in the scope of the invention.

Reference is now made to FIG. 1 which illustrates a device 10 forsterilization of a dental root cavity 12, according to an embodiment ofthe invention. The device comprises an electrode pair 14 for extendinginto the cavity.

A controller—control box 16—comprises a power supply 17, a controller 18and an apex locator unit 19. The power supply includes capacitors tostore energy, a voltage supply, a supply limiter and a timer, andprovides precise pulses. The controller 18 optionally includes amicroprocessor and is able to carry out functions such as measuring apexlocation within the root canal, measuring conductivity and calculatingthe pulses needed for the given conditions, in some embodiments of theinvention.

The controller 16 sends a controlled electrical current at high voltageto the cavity via the electrodes. The controlled current is confinedwithin the cavity since both electrodes are located within the cavity.The energy released carries out the disinfection. The energy releasedcan be of the order of magnitude of 1 to 10 or even 40 Joules we aren'tyet sure, but it will most likely be between 25-40 J, and may becalculated to heat fluid within the cavity within milliseconds to atemperature exceeding 200 or 500 degrees Celsius or at least atemperature exceeding 100 degrees Celsius, to kill any bacteria present.It can be expected that this almost instant heating causes a shock wavewithin the cavity.

It is noted that to heat the root canal volume, typically approximately7 micro liters which has been filled with a water based solution toreach 100 degrees Celsius requires approximately two Joules. Toevaporate the same volume an additional 16 Joules is needed.

The pulse is optionally a pulse modulated high voltage alternatingcurrent whose duration defines the necessary energy levels. The highvoltage and the distance between the electrodes define whether breakdownwill occur, preferably leading to breakdown.

Reference is now made to FIG. 2 which is a detail of FIG. 1 showing theelectrodes of the electrode pair. A first electrode 20 extends axiallywithin a sleeve 22. Sleeve 22 is an insulator. A tip of the firstelectrode 20 extends from the sleeve 22. The second electrode 24 of thepair is coiled around the central axis. The electrode construction ismade thin enough and flexible enough to be inserted into a root canal.In particular the end of the assembly comes to a point to allow forpenetration into the depths of the canal. The head of the axialelectrode, meaning the proximal end, has a larger diameter than thedistal end, and the outer electrode is wound around the axial electrode.The two electrodes are isolated from each other.

In some embodiments of the invention, the first electrode iscontrollably extendable along the axial direction, so that the tip canbe extended or retracted as desired. The result is to vary the length ofa gap between the first electrode and the second electrode and thuscontrol the passage of electrical energy within the canal. The mechanismdefines at least two specific lengths of the electrode gap, providingtwo locations or more in the root canal for releasing energy. Pulses ofenergy often lead to sparks and the location of the spark is generallyin the region between the two ends of the electrodes so that adjustingthe height of the first electrode is a relatively accurate way ofpinpointing the location of the spark and thus providing precisepinpointing of the energy, from which point the energy spreads aroundthe canal to carry out sterilization.

The controller may alter the current or the voltage or the time orlength of the pulses and thus adjust the level of energy released withinthe cavity. Such an energy level adjustment may be carried out inconjunction with adjustment of the location of the electrode so thatgreater energy is provided at the outermost end of the root canal andlesser energy at the narrower apex.

It is further noted that the conical shape of the apex tends to decreaseresistance and increase the energy at the narrow parts of the canal,thus naturally providing the energy level adjustment even withoutartificially intervening.

Furthermore the number of pulses in a pulse train is limited so as toreduce the possibility of unintentional energy release after the devicehas been removed from the root canal.

The construction of the electrode assembly may include a plug 26 whichserves to close the cavity, and helps to keep any liquids inside. Theplug thus prevents release of fluids heated by the spark. In addition,if any kind of toxic fluid is used then it prevents the release of thetoxic fluid into the mouth

In an embodiment, the plug is movable to define a depth to which theelectrode pair extends into said cavity. As shown the plug is locatedover rotatable element 28 which can be screwed along thread 30 toprovide a finely defined length of the electrode assembly. The lengthcan be set to define the distance to the apex of the root canal so as toprevent the electrodes from being extended into the apex.

In an embodiment the cavity is filled with fluid before insertion of theelectrodes, so that the effect of the current is to heat the fluid. Theelectrodes can be used to measure the resistance in the cavity prior tosupply of the current so as to ascertain that the fluid is present. Thecontroller may be set to cut off the current if absence of fluid isdetected. In one embodiment there is no separate measurement activity.The first of a train of spark-causing pulses is generated and if theconductivity is too low then it is inferred that the fluid is notpresent and the remainder of the train is stopped.

The device may be used together with any kind of fluid injector thatinjects the conductive fluid into the cavity.

The conductive fluid may be a salt solution, say between 2 and 20%saline solution. Alternatively, other fluids, such as EDTA or the othersterilizing or disinfecting materials mentioned herein may be used.Alternatively, mixtures of antibacterial and conducting materials orconducting antibacterial solutions are used. In some embodiments, thecavity is filled with a conducting liquid and the electrodes, carryingantibacterial material are inserted into the liquid. The root canalcavity is very small, of the order of about 7 micro liters in volume, sothat very little fluid is in fact present. A small amount of energy canthus heat the fluid very quickly.

As shown in FIG. 2, the central electrode extends beyond both the sleeveand the tip of the outer electrode. A gap between the electrodes ofabout 7-10 mm is initially defined, however the central electrode can beretracted from this initial position to define different length gapsduring the course of the treatment. As mentioned above, the sparkgenerally begins in the region between the two electrodes and thusretraction of the central electrode moves this region and allows forsparks at different locations in the root canal. Since the initialmaximum extent is set not to reach the apex, all further treatment issafely away from the apex as well. The spark location can be safelymoved within the canal under complete control. Furthermore the amount ofenergy can be varied according to the present depth. In the deepestparts of the canal the diameter is much smaller and thus less energy isneeded than say at the surface.

The amount of power may be arrived at by online measurement of thecurrent and voltage during the pulse train. The constricted space of thecanal can only accommodate a limited amount of energy, and increasingthe amount of energy beyond this value achieves nothing. However, sinceincreased energy causes heating of the tooth, higher energy inputs maynot be desirable. The pulse energy level may thus be limited to thelowest value giving such an upper resistance value for any reason.

-   -   Controlling according to the upper resistance value provides for        greater energy for greater width and less energy for lesser        width.

Overall, a preferred diameter for the central electrode is 0.15 mm. Thespiral shape of the second electrode may serve to increase thestructural stability of the electrode assembly as a whole.

The device may include an apex locator detection unit which detects theapex of the root canal. Such an apex detection unit is discussed inapplicant's copending US Patent Application Publication No. 2008/0187880A1, the disclosure of which is incorporated by reference. However, anyapex detector, as known in the art, may be used in some embodiments ofthe invention. Alternatively, no apex measurement is made by system 10.Plug 26 serves as a mechanical limiter to limit an extension of saidelectrode pair into the detected apex.

The controller 16 may comprise a pulse generator and the current may becontrolled by varying a size of the pulses generated.

As mentioned, measurement of the resistance measurement between theelectrodes is useful for a number of purposes. Thus the controller mayinclude a resistance measurement unit which measures electricalresistance around the extent of the electrode pair. The controller mayshut off the controlled current to the electrodes whenever theelectrical resistance is at a level indicating that the electrodes arenot currently located in the cavity or are located in an apex of saidcavity, or when the fluid does not appear to be present.

In an embodiment, the controller supports a pre-disinfection stage ofcavity clearing, in which pre-treatment pulses from the electrodes cleardead or dying tissue from the root canal or the walls. Such apre-disinfection stage may be carried out without artificial insertionof fluid, more specifically prior to insertion of the fluid into theroot canal. The natural moisture in the canal may be sufficient. Asshown in FIG. 1 (and in greater detail in FIG. 6), the plug 26 is placedover the tooth being treated. Handle 32 is held by the operator to keepthe electrode assembly steady within the root canal and button 34 ispressed both to start a train of pulses and to operate the retractionmechanism of the central electrode, so that the pulses can be spread outover at least two locations over the length of the canal.

Reference is now made to FIG. 3A, which is a cross section showing themechanism of device 10, according to an embodiment of the invention.Parts that are the same as those in figures already described are givencorresponding reference numerals and are described further only asnecessary for an understanding of the present embodiment. FIG. 3Aparticularly shows the details of the mechanism for advancing theelectrode. Electromagnet 36 is alternatively energized and de-energizedto attract or not attract pole 38. Pole 38 takes with it block 40 whichis pulled upwards until it reaches step 41, where it is stopped. Thearrangement provides for two electrode positions, an upper position anda lower position, as illustrated in FIG. 8 below. The length of slot 42is chosen for optimal location of the spark along the root canal. Spring43 ensures an electrical connection to the outer electrode irrespectiveof the position of the electrode. Button 34 allows the user to operatethe controller which will operate the control of the electromagnet andthus the position of the electrode.

Reference is now made to FIG. 3B, which is a simplified cross-sectionillustrating a variation of the mechanism of FIG. 3A in which a steppermotor allows a larger number of electrode positions to be attained.Parts that are the same as those in figures already described are givencorresponding reference numerals and are described further only asnecessary for an understanding of the present embodiment. Stepper motor44 receives commands from the controller and rotates accordingly. Block45 rotates and via the mutual thread arrangement advances or retractspole 46 accordingly in a controlled manner.

Reference is now made to FIG. 4, which shows that the device may beconstructed in three parts, the insertion head 50, which includes theelectrode assembly and the cap, the electrode control unit 52 whichincludes the cap mechanism and the plunger mechanism, and the handleitself 54, which is angled for ease of use. The electrode assembly maybe removable for sterilization in an autoclave

FIG. 5 illustrates an embodiment of a working device. The sterilizationdevice 10 is one of three attachments to a main controller 60 and isinserted into the root canal where electrical sparks are used tosterilize the root canal. Hook 62 is looped on the lip and thecombination of hook 62 and attachment 64 are used for locating the apex,in conjunction with the apex location unit.

FIG. 6 is an enlarged diagram showing the electrode assembly insertedinto the root canal. Plug 26 both seals liquids within the tooth cavityand acts as a limiter to prevent the electrodes from reaching the rootcanal apex. The axial electrode 20 has an exposed tip portion 70. Thecoiled second electrode 24 has a tip 74. The distance between the tip 74and the beginning of the exposed portion 70 defines a spark gap, and itis this distance which is varied by moving the axial electrode so thatthe precise location of the spark can be varied during the therapy asdescribed above in respect of FIGS. 3A and 3B. The sleeve is fixed withthe electrode assembly 50 which is fixed in place by holders 71.

A prototype using the above energy levels managed to sterilize a rootcanal having a high concentration of bacteria, of the order of 10⁻⁶,which is equivalent to a highly infected root canal.

A process for use of the device is now described with respect to FIG. 7.The process begins with stage 80 by locating the apex using the apexlocator attachment 19 and hook 62. Alternatively, the location of theapex (referenced to the top of the tooth) is determined using a separateapex locator. At the same time as the apex is located the moisture levelof the root is measured and fed directly into the operating program. Instage 82, plug 26 is then rotated to define the depth of the apex so asto act as a guard against the electrodes being inserted into the apex.Preferably the plug is set to give a predetermined distance of clearancefrom the apex, one or two or more millimeters of clearance. For example,initial clearance of 3-4 millimeters appears to be suitable.

An intermediate stage 84 of providing an initial pulse based on partialpenetration of the electrode device into the canal can optionally becarried out in order to dry the tissues of the canal which will need tobe removed by the files prior to sterilization. Drying the tissues easestheir subsequent removal. The size of pulse needed to dry the tissuesmay be obtained from the detected moisture level of the canal asdetected previously.

The optional conductive and/or cleaning and/or disinfecting fluid may beinjected into the root canal in stage 86.

The electrode assembly is now attached to the handle and inserted intothe channel until further progress is impeded by the plug, in stage 88.In some embodiments of the invention, the electrode assembly is dippedin a disinfectant or antibacterial material before being inserted intothe liquid in the root canal.

The dentist then presses on the button 34, which operates the controlprogram in the controller. The control program issues one or more pulsesof defined power depending on the location of the electrode within thecanal and the size of the canal—the apical constriction. When the volumeof the canal is lower, the power in the pulses will be lower. Thevoltage level of the pulses is controlled to affect the overall power asis the timing of the pulses. The pulse train may stop when the programis completed. As a safety feature, in an embodiment of the invention, asingle push-button operates the system, with a first push of the buttoncausing a set of capacitors to charge and a second push causing thecapacitors to discharge into the cavity. As an additional safetyfeature, a waiting period between pulse trains is preferably required,for example a wait of 45 seconds between pulse trains. A typical numberof pulses for the train would not exceed four although it is envisionedthat a larger number such as 6 could be used. Between pulse trains, theroot canal is preferably rinsed and refilled with liquid.

Once the control program has completed the train of pulses for thedeeper part of the root canal—stage 90, the plunger is operated to movethe electrodes to the higher part of the canal, further from theapex—stage 92. In stage 94 a further pulse train is produced, and heregreater power is used as the size of the canal is larger. If neededadditional liquid is added and/or the electrode assembly is dipped indisinfectant or antibacterial material before stage 94. As mentioned theamount of power is arrived at by online measurement of the current andvoltage. The pulse energy level may thus be limited to to a value givinga desired energy.

Finally, in stage 96, a large pulse is optionally supplied to disablethe electrodes and stop further activity. The large pulse is a safetyfeature intended to ensure that electrical energy is not inadvertentlyreleased outside the root canal, say in contact with the jaw or themolars.

A further safety feature involves the ability to detect inadvertententry of the electrodes into the apex for whatever reason, say humanerror in setting the plug. The apex locator mechanism continuallyoperates via a small current through the electrode 20 sent to hook 62,of the order of 10 mA. A danger area is defined and whenever theelectrodes are indicated to be in that danger area the pulse train isautomatically shut down.

An additional safety feature ensures that the actual energy of the pulsedoes not exceed the calculated energy.

Reference is now made to FIG. 8 which illustrates the device of thepresent embodiments in two pulse positions in the root canal The deviceis initially extended as far as plug 26 will allow, which means that theelectrode reaches deep into the root canal, and almost up to the apex.The first pulse or pulse train is issued at this first deepposition—position A. Then the electrode is retracted, for example usingthe mechanism of FIG. 3A above, and the second pulse or pulse train isemitted at position B. Optionally, a single pulse train or multiplepulse trains at a single position (for example, 3-4 mm from the apex) issufficient to provide sterilization.

A device according to the present embodiments may have a number ofadvantages over the existing systems that use electrodes.

First of all there is no heating of tissues outside the root canal.Rather all the energy is concentrated in the region that requiressterilization. Furthermore there is no nerve stimulation outside theregion of treatment. Thirdly there is no need to subject the patient tothe psychological trauma of having the other electrode clearly in viewand being felt. Furthermore the safety features that are needed arefewer than for the existing devices.

As a further safety feature, the energy of the pulse is limited by theupper resistance threshold of the cavity.

FIG. 9 is a simplified schematic diagram which shows use of attachmentsfor apex location in order to set the plug. Parts that are the same asin earlier figures are given the same reference numerals and are onlyexplained again in accordance with the need to understand the presentfigure. The process of locating the apex is controlled within controller60. Hook 62 is placed on the gum to define a ground and then a train ofhigh frequency pulses are released into the canal from apex locationattachment 64. The reflection of the pulses is measured. A second trainof pulses is then emitted at a different frequency and the reflection ismeasured. The two reflections are subjected to signal processing andthen applied to a look up table which supplies a number, that numberbeing the length of the canal. The user then sets the plug to give anelectrode length according to (in fact slightly less than) that numberin millimeters. The preferred process is more fully described inapplicant's copending International Patent Application No.PCT/IL2007/000755, the contents of which are hereby incorporated byreference.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims. All publications, patents, and patentapplications mentioned in this specification are herein incorporated intheir entirety by reference into the specification, to the same extentas if each individual publication, patent or patent application wasspecifically and individually indicated to be incorporated herein byreference. In addition, citation or identification of any reference inthis application shall not be construed as an admission that suchreference is available as prior art to the present invention.

What is claimed is:
 1. A method of treatment of a root canal having alongitudinally variable diameter and longitudinal curvature within atooth comprising: filling said root canal with a disinfectant fluid;inserting an insulator and a pair of electrodes into said root canal andsaid disinfectant fluid, said pair of electrodes including an outerelectrode external to said insulator and exposed to said fluid along alength of said insulator and a second electrode said second electrodeincluding an insulated portion located within said insulator and anexposed portion extending distally from a distal end of said insulatorinto an apical portion of said root canal and exposed to thedisinfectant fluid; generating an electrical energy pulse creating aspark in the disinfectant fluid along a length of the canal between saidouter electrode and said exposed portion of said second electrode. 2.The method of claim 1 wherein the method includes winding said outerelectrode around said insulator.
 3. The method of claim 1, wherein theenergy pulse causes a breakdown in the root canal in a gap of between 7to 10 mm between said exposed portion of said second electrode and saidouter electrode and is limited to the root canal.
 4. The method of claim1 wherein the energy pulse causes a breakdown in the root canalgenerally along a length of the canal, that is limited to the rootcanal.
 5. The method of claim 1, further comprising measuring a locationof an apex of said root canal; setting a mechanical limiter to provideinsertion of said exposed portion of said second electrode a controlleddistance into said root canal, responsive to said apex locationmeasurement; and moving said pair of electrodes in relation to saidlimiter.
 6. The method of claim 5, further comprising: closing the canaland keeping liquids inside the canal by means of a plug and wherein saidlimiter includes said plug.
 7. The method of claim 1, further comprisingcontrolling said energy pulse according to a local volume of said rootcanal between said outer electrode and said exposed portion of saidsecond electrode.
 8. The method of claim 7, comprising locating saidouter electrode at a first depth in said root canal and providing theenergy pulse thereat and then relocating said outer electrode to asecond depth while said disinfectant fluid remains in the canal andproviding a further energy pulse at said second depth.
 9. The method ofclaim 1, wherein said disinfectant fluid includes a salt solution. 10.The method of claim 9, wherein said salt solution comprises a saltconcentration lying between 0.9% and saturation.
 11. The method of claim1 wherein said disinfectant fluid comprises one or more of hydrogenperoxide, EDTA, chlorhexidine or iodoform (IKI—potassium iodide). 12.The method of claim 1, further comprising providing an electrical pulseto dry tissue from the canal before said filling, said generating andsaid disinfecting.
 13. The method of claim 1, further comprisingretracting said second electrode to adjust a length of a gap betweensaid outer electrode and said exposed portion of said second electrode.14. The method of claim 1, wherein said outer electrode is fixed to saidinsulator.
 15. The method of claim 1, further comprising: increasing astructural stability of the insulator and second electrode with saidouter electrode.
 16. A method of treatment of a root canal having alongitudinally variable diameter and longitudinal curvature within atooth comprising: inserting a flexible pair of electrodes with aninsulator into a fluid in the canal, said pair of electrodes includingan outer electrode external to said insulator and exposed to said fluidalong a length of said insulator and a second electrode, said secondelectrode including an insulated portion located within said insulatorand an exposed portion of the second electrode from a distal end of saidinsulator into an apical portion of said root canal and exposed to thefluid; generating an electrical energy pulse between said outerelectrode and said exposed portion of said second electrode; limitingsaid energy pulse to an amount of energy that can be accommodated by aconstricted space of the canal; causing a breakdown of fluid within theroot canal as a result of said energy pulse; producing a pressure wavewithin said root canal as a result of said breakdown; forcingdisinfecting material in said fluid by means of said pressure wave intoa channel not open to said any of said outer electrode and said secondelectrode; and disinfecting said channel utilizing said breakdownwherein said disinfecting material is limited to the root canal andchannel.
 17. The method of claim 16, further comprising providing anelectrical pulse to dry tissues within said root canal for removal ofsaid tissues before said generating and said disinfecting.
 18. Themethod of claim 16, further comprising: varying a length of a gapbetween said exposed portion of said second electrode and said outerelectrode according to the constricted space of the canal while saidouter electrode and said exposed portion of said second electrode areinside said canal.
 19. The method of claim 16, wherein said outerelectrode is fixed to said insulator.
 20. The method of claim 16,further comprising: increasing a structural stability of the insulatorand second electrode with said outer electrode.